Great hotel! Though not actually in the historic town center, it is an easy walk from the hotel to the old town (about 10-15 minutes), through a lovely shopping area. Following in the tradition of recent new-build European Sheratons (Porto, Prague), the Sheraton Poznan gets an A from me for interior design. The check-in staff were also exceptionally friendly. I was upgraded in advance to a Junior Suite, which was quite nice. Below are some photos of the room:
Junior Suite Bedroom
Junior Suite Work Desk
Junior Suite Living Room (And Complimentary Bottle of Malbec!)
Junior Suite Bathroom
Junior Suite Tub and Rainfall Shower
Also, as for Poznan itself, the historic town center is fairly compact, and you can see pretty-much everything in a day. I wouldn't recommend it for an extended vacation, but it's definitely worth planning a day-trip, if you are in the general vicinity. The town center is very pretty, and well worth seeing:
Main Square
Ratusz at Night
Parish Church of St. Stanislaus (simply gorgeous!)
Domed Ceiling of Parish Church of St. Stanislaus